368 Produce Degradation: Reaction Pathways and their Prevention
11.2.8 RODENTICIDES AND AVICIDES
Rodenticides are intended to kill vertebrate pests, mainly rodents, which may cause
significant damage in produce production and storage and also pose a great risk to
human and animal health. The application of rodenticides must be carefully moni-
tored because they are also highly toxic to humans and domestic and other nontarget
animals. In special situations, fumigants, such as hydrogen cyanide, phosphine,
sulfur dioxide, or methyl bromide are used to control rodents (and many other pests)
in enclosed spaces (warehouses, etc.) or their burrows [1]. However, rodenticides
are more generally applied as baits; the most popular active ingredients include zinc
phosphide, strychnine, sodium fluoroacetate, fluoroacetamide, chloralose, and vari-
ous coumarin or indandione anticoagulants [1,5].
Zinc phosphide reacts with stomach acids to liberate toxic phosphine, which
enters the bloodstream and affects liver, kidney, and heart functions. Strychnine is
one of the oldest rodenticides that is still being used. This naturally occurring alkaloid
(extracted from seeds of Strychnos spp., Loganiaceae family) acts as an antagonist
of the neurotransmitter glycine. The toxicity of the sodium salt or amide of fluoro-
acetic acid (sodium fluoroacetate or fluoroacetamide) arises from its role in the
biosynthesis of fluorocitrate, which inhibits the enzyme aconitase in the tricarboxylic
acid (Krebs) cycle. Anticoagulants, such as brodifacoum, bromadiolone, chloropha-
cinone, difenacoum, or warfarin, interfere with the action of vitamin K, thus blocking
the formation of the blood clotting factor prothrombin, so that a minor injury can
cause a fatal hemorrhage (the indandione anticoagulant chlorophacinone also uncou-
ples oxidative phosphorylation). Chloralose is primarily a sleep-inducing narcotic
drug that acts by retarding metabolism and lowering body temperature to a fatal
level (causing hypothermia). Chloralose can also be used as a relatively low-hazard
avicide, enabling pest birds to be caught and killed by other means.
Pest birds represent another problem in produce production because they may
lower yields and quality and cause surface damages. Moreover, their droppings can
pose a health risk to consumers. Because of environmental and wildlife concerns,
bird control using avicides and bird repellants should be avoided and other means,
such as frightening and restriction devices, preferably should be used [77]. Thus,
avicides are more often applied around public buildings in cities than in crop fields.
In addition to chloralose, 4-aminopyridine (Avitrol) is another compound used in
bird control; in essence it serves as a bird repellant because it may affect only a few
members of a flock, causing them to become hyperactive, thus frightening away
other birds [78].
11.2.9 PLANT GROWTH REGULATORS
Plant growth regulators (PGRs) are substances that can control (accelerate or retard)
plant growth; initiate flowering; induce fruit setting; control fruit maturation; stim-
ulate root development; cause blossoms, fruits, and leaves to fall; or delay fruit drop.
Thus, PGRs may significantly improve produce yields and quality (size, shape, color,
etc.). They can also be used as herbicides, sprouting inhibitors, defoliants, and fruit
thinning agents.